1. Field of the Invention
The present invention relates to credit card-sized electronic assemblies, and more particularly, to credit card-sized modems.
2. Related Art
Credit card-sized electronic assemblies are gaining importance with the expanding portable computer market. These small electronic assemblies, which are sometimes referred to as PCMCIA (Personal Computer Memory Card International Association) devices, plug into equipment such as a portable computer to provide additional features such as extra memory, extra programming, modem capabilities or facsimile capabilities. The PCMCIA devices slip into a port or opening in the computer which conforms to the physical standards set by the PCMCIA. A connector at one end of the PCMCIA device is used as an interface to the personal computer.
In the case of a PCMCIA modem or facsimile device, another connector, at the opposite end of the device, is used as an interface to external equipment such as a telecommunications network (telephone line) or a cellular communications interface circuit. The conventional credit card-sized modem includes modem circuitry and a DAA (data access arrangement) circuit. The DAA circuit provides an interface between the modem circuitry and a telephone line. For example, the DAA provides high voltage isolation, amplification, current limiting, impedance matching, and meets other electronic compatibility requirements.
While the PCMCIA has provided standards for the physical requirements of these credit card-sized modems, the telecommunication interface requirements of the DAA circuit is not governed by one international entity. As a consequence, countries have very differing requirements that the DAA circuit must meet. For example, the Federal Communications Commission (FCC) and Underwriter's Laboratories Inc. (UL) set standards which DAA circuits in the United States must meet. Other countries have differing standards.
It is desirable to produce a PCMCIA modem which may be used in different countries. However, a DAA assembly which meets the requirements of all countries is not currently available. One conventional solution to this problem is to use an external DAA circuit. As stated above, the PCMCIA modem includes an external connector for interfacing the modem to a telephone line. The DAA assembly is implemented as an integral part of the cable (known as a "bump" in the cable implementation) which connects the modem to the telephone line. Different cables, each including a different DAA circuit, could then be used to meet differing international requirements. Several cables could be carried, for example, in the carrying case of a portable computer. Other approaches have used an external DAA assembly which plugs into a connector at the back of the PCMCIA modem.
These conventional solutions include a variety of disadvantages. For example, with the bump in the cable approach, it is cumbersome for a user to carry several large cable/DAA assemblies. With the external DAA assembly which plugs into a connector at the back of the PCMCIA modem, the DAA assembly will protrude from the computer and must be removed before transporting the computer. What is needed is a PCMCIA modem which is easily adaptable to differing national telecommunication standards and which overcomes the limitations of conventional devices.